1. Field of the Invention
This invention relates generally to the field of elevator controls, and in particular, to illuminated call button and/or annunciator assemblies and circuits for elevators, which are subject to vibration during operation.
2. Description of Art
Switches and circuits for elevator controls can experience premature failure due to the vibration which is inherent in elevator operation. Switches and circuits for elevator controls can also experience premature failure due to the repeated mechanical stresses and the repetitive surge currents which develop as the call buttons, for example, are pressed and even sometimes punched, on a daily basis. Call buttons are deemed to include those buttons which are mounted outside the elevator doors, adjacent thereto, as well as those in the elevator cabs. When lighted indicators are required, but without a switching capacity, it is customary to use a call button assembly with a lamp but without switches. Such indicators are referred to as annunciators. Hereinafter reference will be made generally to call button/annunciator assemblies as encompassing all of these variations of the elevator call button.
Call button/annunciator assemblies have been constructed with smaller and smaller components over the years, following the general trend in electronics towards miniaturization. Smaller and smaller switch assemblies have been developed, which can result in lower costs of manufacture. Unfortunately, such smaller switch assemblies, particularly illuminated switch assemblies, are less resistant to the wear and tear of the vibration and the mechanical and electrical stresses.
Although some savings can be realized in cost and manufacture, the cost saving is illusory. As a practical matter, a service call by a trained technician is necessary to change a lamp in a call button/annunciator assembly. Even if the cost of the miniature or subminiature lamp, for example $1.50, is discounted altogether, the minimum charge for such a service call can be Fifty to Seventy dollars, on average.
Construction practices in the industry been undertaken which have reduced the initial cost of call button/annunciator assemblies by utilizing lamps which can be coupled directly to an AC mains source, albeit through one or more switches. This substantially increases the premature aging effects of surge currents each time the lamp is lit, particularly in high voltage installations, for example those over 60 volts, which constitute the majority of all installations. The effects of surge currents further reduce the operational lifetime of the lamp, necessitating more service calls. Tungsten filaments in lamps are subject to a phenomenon known as notching, which is the appearance of step-like or sawtooth irregularities, on all or part of the tungsten filament surface. The phenomenon is more pronounced in smaller lamps, which are manufactured with thinner filaments. Thinner filaments are also more prone to damage from mechanical stress or shock. Experience has shown that lamps are the weakest link in the maintenance chain from elevator call button/annuciator assemblies. Indicator assemblies employing neon lamps and light emitting diodes have proven unsatisfactory, being too dim and being incapable of emitting white light.
This invention deals with the real problem plaguing call button/annunciator assemblies for elevators, which is not reducing the initial cost of manufacture, but significantly extending the operational lifetime of such assemblies by reducing the frequency of service calls needed to change burned out lamps. Several measures are taught herein to extend the operational lifetime of lamps in elevator call button/annunciator assemblies. When these measures are undertaken, the operational lifetime of a lamp can be increased from a range of eight months to one year to a range of three to five years.
Firstly, these measures include the use of wedge-based lamps, which have been proven reliable in vibration environments in other fields. Secondly these measures include the use of larger lamps having larger and thicker filaments, which are less prone to notching or other damage from surge currents or mechanical stresses. Thirdly, these measures include incurring the added cost of a transformer for driving each lamp at a significantly lower than AC mains voltage level, and to enable use of a lamp which is rated for a higher voltage than the secondary output of the transformer, but lower than the AC mains voltage. As an example, a 120 volt mains supply, which would otherwise energized a lamp directly, is stepped down to a 24 volt secondary supply voltage by the transformer to drive a wedge-based lamp rated for operation at 28 volts. Fourthly, these measures include a modular push-button assembly for implementing an elevator call button/annunciator assembly, which is adapted to accommodate a larger bulb without significantly increasing the size of the assembly housing and to streamline production.